The present invention relates to a spectroscopic instrument, which performs spectroscopy based on a reflection light from an object to be measured.
In building structures such as bridges, tunnels, and the like, a large amount of concrete is used on leg portions, wall surfaces, and the like. The concrete deteriorates over time due to salty substances in the atmosphere or the like. Therefore, as a purpose of maintenance operation, it is necessary to periodically measure the salinity concentration in the concrete and to judge the degree of deterioration of the concrete.
A spectroscopic instrument is known as an instrument for measuring the salinity concentration in the concrete on a non-contact basis. The spectroscopic instrument can measure the salinity concentration in the concrete by projecting a near-infrared light to the concrete and by analyzing the reflection light from the concrete, and the degree of deterioration of the concrete is judged based on the salinity concentration.
As a light source to be used by the spectroscopic instrument, a halogen lamp, a halogen heater, and the like can be given, for instance. In a case of the halogen lamp or the halogen heater, the light as emitted includes the near-infrared light with a wavelength of about 0.8 μm to 2.5 μm, and has stability with respect to temperature change and the like. Further, the halogen lamp or the halogen heater is suitable as the light source of the spectroscopic instrument since a measurable amount of light can be obtained even in a case where the distance from the light source to the object to be measured is about 10 meters.
In the spectroscopic measurement, it is necessary to obtain a high wavelength resolving power in order to improve measurement accuracy. However, in a case where there is chromatic aberration in an optical system, a focal length changes per each wavelength, and there is a possibility that a curve of spectral characteristics may change per each distance. Therefore, there is a possibility that the chromatic aberration may become a hindrance to the improvement of the measurement accuracy.
Further, conventionally, in order to correct an influence of chromatic aberration, a measurement is carried out per each distance regarding a predetermined reference diffusing reflecting object and stored as a reference value in advance, and the influence of the chromatic aberration is corrected by comparing the measurement results with the reference value corresponding to the distance to the object to be measured, when the measurement is carried out. Therefore, it took a lot of working time and working efficiency was low.